问题
I am trying understand about the size that a Java object will be allocated with when created using a new operator.
Consider that i am creating a class
public class NewClass {
NewClass() { }
}
when i create an instance of NewClass using NewClass nc = new NewClass();. what is the size of the NewClass that gets created in the heap?
~ Jegan
回答1:
Profiling is the best way, but you can get a good estimate like so:
8 bytes per object (bare overhead), plus fields.
- Primitive Fields: as listed in Java. Note: booleans need 1 full byte.
- Object fields: 1 pointer (4 bytes on 32-bit VM, 8 on 64-bit), plus size of object itself (if not a reference to a preexisting object)
- Arrays: 4 bytes + object/primitives for elements
- Strings: far, far too much. IIRC, 24 bytes + 2 bytes/character. Might be more.
The final result is increased to the nearest multiple of 8 bytes.
See also my example here for how to calculate memory use on a more complex object. Note: these rules may vary with VMs, and may change as newer versions of the VM come out. My estimate only applies to the Sun JVM, although I suspect IBM's results will be similar.
回答2:
I think you need to use a profiler to measure this. You may use JProfiler or YourKit profilers for this.
来源：https://stackoverflow.com/questions/2062553/java-object-creation-and-memory-size